This image shows a crescent Uranus, a view that Earthlings never witnessed until Voyager 2 flew near and then beyond Uranus on January 24, 1986.

Following its flybys of Jupiter and Saturn, Voyager 2 was to become the first -- and only -- spacecraft to visit Uranus. The planet displayed little detail, but gave evidence of an ocean of boiling water about 800 km below the cloud tops. The spacecraft discovered 10 new moons, two new rings, and a strangely tilted magnetic field stronger than that of Saturn.

This planet's natural blue-green color is due to the absorption of redder wavelengths in the atmosphere by traces of methane gas. Uranus' diameter is 32,500 miles, a little over four times that of Earth. The hazy blue-green atmosphere probably extends to a depth of around 5,400 miles, where it rests above what is believed to be an icy or liquid mixture (an 'ocean') of water, ammonia, methane, and other volatiles, which in turn surrounds a rocky core perhaps a little smaller than Earth.